DE 25 07 138 (U.S. Pat. No. 4,044,234) discloses measuring the angular velocity in a given angular interval before the top dead center and the angular velocity in a same angular interval after the top dead center of a cylinder situated in the expansion stroke. If the difference between the two values falls below a specified threshold value, it is concluded that the combustion in the monitored cylinder has failed. The mentioned differential measurement is performed for all the cylinders of an internal combustion engine. When one of the differential values falls below the specified threshold value, a misfiring is recognized.
Measurements for individual cylinders are also performed in a process as described in an article by I. Geiger al titled "Running Irregularity an Input Variable for Control Processes" in the conference report for the 8th Viennese Motor Symposium 1897, S. 277-295. A measurement is performed for each cylinder in an angular interval after the top dead center for three successive expansion strokes V1, V2 and V3. The time period T.sub.-- V1, T V2 or T.sub.-- V3 in which the crankshaft rotates by a specified angular interval is always measured. The runningirregularity value LUW is calculated according to the following formula: EQU LUW=f(T)x.vertline.(T.sub.-- V2-T.sub.-- V1)-(T.sub.-- V3-T.sub.-- V2),.vertline. (1)
whereby: f(T)=1/T.sub.-- V1.sup.3 or 1/(T.sub.-- V1x T.sub.--V 2x T.sub.-- V3)
The thus calculated running-irregularity value is applied in an idle speed control.
Unlike the above-mentioned processes, runningirregularity values are able to be determined not by applying successive expansion strokes of a same cylinder in the equation (1) indicated above as expansion strokes V1, V2 and V3 in which measurements are performed, but rather by applying immediately successive expansion strokes. Such a process is described in an article by V. Bianchi et al. titled "A Simple and Objective Process for Measuring Irregular Running" in MTZ 39/1978, Nr. 7/8, S. 1-5. The mentioned article does not specifically describe processes which make use of calculated runningirregularity values.
In practice, however, the process just mentioned leads again and again to false information, since the influences of the road and gear unit prove to be disturbing. Therefore, one has been confronted for quite some time with the problem of specifying a more reliable process for measuring running irregularity.